We studied the effects of heat treatment on single-walled carbon nanotubes (SWNTs) aligned on a sapphire (α-Al2O3) substrate to understand the interaction between the SWNTs and sapphire. The Raman measurements showed a clear upshift of the G-band after heat treatment at 1000°C in a high vacuum. Furthermore, Auger spectroscopy showed an increase of the [Al]/[O] atomic ratio of the sapphire surface upon heat treatment, indicating the removal of oxygen atoms from the sapphire surface. The observed upshift of the G-band is accounted for by the hole doping to the aligned SWNTs from the oxygen-deficient sapphire substrate. This annealing-induced carrier doping from the underlying substrate would offer a new and unique approach to modify the electronic structure of SWNTs.
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